The use of standardized bulk containers, for example standardized sea bulk containers, to transport bulk solids is widely accepted. To preserve the cleanliness of the solids or to avoid leakages, the bulk containers are generally equipped with inner liners in which the solids to be transported are stored. This system, commonly referred to as “bag-in-the-box”, allows to save packaging operations and avoids to transport packaging materials. The inner liners are made of a flexible material as for instance polyethylene or polypropylene.
When the solids are unloaded from a container equipped with an inner liner, measures have to be taken to preserve during the unloading the benefits brought by the inner liner. For instance, unloading by just tilting the container and pouring the solids on the floor is not acceptable in view of the possible contact of the solids with outside contaminants.
One known solution is to use inner liners provided with a coupling device, which itself is coupled to a closed pneumatic delivering system. The pneumatic delivering system unloads the solids directly in silos, where they are well contained and protected from possible contaminations coming from the environment.
However, when the solids are in the form of powders and in particular in the form of powders having a high angle of repose, it is often difficult to maintain a steady state flow rate to the pneumatic delivering system. Blocking often occurs, which requires the opening of parts of the coupling device or of the pneumatic tubing, thus reducing the advantages of the whole process.
In WO2009/130271 is described a method of unloading a powder from a container. In this method the lower part of the powder in the container is aerated by injecting gas in it. The aerated powder has a lower angle of repose and flows more easily in the discharge opening of the liner. The required tilting angle of the container during unloading is also reduced.
This known method, while efficient for unloading free flowing powders, appears insufficient for some powders, in particular those having a high angle of repose.